Governors or limiters have been developed and utilized to manage various aspects of vehicle operation. Whether mechanical or electronic, governors are often used to limit one or more operating parameters to achieve a goal such as protecting vehicle components, maintaining safe vehicle operation, or improving operating efficiency. For example, an engine speed limiter or governor may impose an upper limit on engine speed to prevent damage to various engine or vehicle components. A vehicle speed or road speed limiter may impose an upper limit on the ground speed of the vehicle in an attempt to restrict unsafe operation of the vehicle.
A road speed (or vehicle speed) limiter may also be used in commercial vehicles, such as MVMA Class 7 and Class 8 vehicles, to reduce the adverse impact of increased speed on fuel economy. Such vehicles typically have significant aerodynamic drag which increases as a cubic function of vehicle speed. As such, fleet operators attempt to reduce operating costs by balancing the complementary factors of trip time and fuel consumption by imposing a road speed limit on vehicle operators. However, many vehicle drivers have objectives different from those of the fleet operators. As such, drivers may attempt to defeat or bypass various governors in an effort to increase vehicle power and/or speed, and thereby decrease trip time at the expense of fuel consumption.
Tampering with the vehicle speed sensor has become a significant issue with many on-highway vehicle fleets. Current engine or powertrain controllers employ various methods to detect a shorted or open vehicle speed sensor (VSS) circuit. For example, a malfunction code may be generated when the pulse width of the fuel signal is greater than a calibratable number of degrees, engine speed is greater than a calibratable RPM, and measured vehicle speed is less than a calibratable limit for a predetermined amount of time. When such a failure is detected, precautionary measures may be employed such as limiting the rated engine speed to the equivalent RPM for the road speed limit value in the highest or top gear (lowest input to output gear ratio). To avoid triggering a fault condition by disconnecting the VSS, drivers may connect a fixed frequency oscillator such as those utilized in dimmer controls to defeat the vehicle or road speed limiter. An artificial speed sensor signal having a fixed frequency, or a frequency which is based on engine speed may result in the vehicle controller calculating an artificially low vehicle speed thereby allowing high speed operation with commensurate poor fuel economy and possibility of unsafe operation.